A type of cutter in common use is a single saw blade cutter with an abrasive wheel cutting blade or a metal cutting blade; during cutting, this will exert a pushing force on the workpiece in the direction of rotation of the cutter, and a corresponding clamping force must be applied to the workpiece in order to ensure that the cutting work progresses smoothly. Although such a common single saw blade cutter is also able to achieve the cutting objective, such a cutter has low operational efficiency, the cutter blades thereof wear quickly, and it is moreover dangerous to operate. For these reasons, people have designed a cutter with twin saw blades; for instance, the “dual saw blade cutter” with Chinese patent grant announcement no. CN2728685Y has disclosed just such a tool, which comprises a machine body and a machine head, the machine head further comprising a guard, a head shell, an inner saw blade, an outer saw blade and a drive mechanism, wherein the drive mechanism is further composed of an output shaft, a sleeve shaft, a first gearwheel, a second gearwheel and a power gear shaft; the sleeve shaft is sleeved onto the output shaft and fixed on an end cover by means of a pair of sleeve shaft bearings, the first gearwheel is fixed on the sleeve shaft, the second gearwheel is fixed on the output shaft, the teeth of the power gear shaft are engaged with the first and second gearwheels respectively, the inner saw blade and an inner pressure plate are sleeved successively on an outer end section of the output shaft, with the inner saw blade being pressed on an outer end face of the sleeve shaft by the inner pressure plate; the inner pressure plate and the output shaft are connected together by a socket connection therebetween, and the outer saw blade is fixed on the output shaft by an outer pressure plate and the inner pressure plate. In the twin saw blade cutter employing the above structure, the fact that the direction of rotation of the inner saw blade is opposite to that of the outer saw blade during operation means that cutting resistance during the cutting process is small and the forces on the workpiece are small, and therefore the workpiece clamping force is small, operational safety is good, and cutting noise is low, and it is also distinguished by high cutting efficiency and a flat cutting surface.
However, during actual operation, the above twin saw blade cutter will manifest the following deficiencies: (1) As a result of cumulative error in machining of the assembly components, the output shaft will have a certain degree of axial play, which will cause the outer saw blade to have axial play, with the end result that the smoothness of rotation of the inner and outer saw blades will be affected. (2) The power gear shaft forms a drive pair which is a spiral bevel gear set with the first gearwheel and the second gearwheel respectively, and these rotate in forward and reverse directions around the same center of rotation; this structure results in the power gear shaft always having the tendency to be displaced axially towards the side of the first gearwheel and the second gearwheel when it is rotating, and thus after a long period of operation, wear between the power gear shaft and the first and second gearwheels will be accelerated; in serious cases, proper meshing will become impossible and the phenomenon of free spinning will occur. (3) The method of mounting the inner and outer saw blades cannot ensure the coaxiality and perpendicularity of the saw blades relative to the center of rotation. (4) Since the outer saw blade is fixed on the output shaft by the outer pressure plate and the inner pressure plate, and the inner pressure plate and the output shaft are made as a split-type structure, which split-type structure will affect the mounting position of the outer saw blade on the output shaft, the smoothness of cutting of the two saw blades will be affected as a result.
Content of the Utility Model
The technical problem which the present utility model seeks to solve is to provide a twin saw blade cutter capable of effectively avoiding axial play in the small output shaft in response to the current technical situation described above, and thereby enable the relative positions of the inner and outer saw blades to be ensured, such that cutting work can proceed smoothly.
The technical solution employed in the present utility model in solving the above technical problem is: the twin saw blade cutter comprises a machine body and a machine head, the machine head further including a gearwheel box, an inner saw blade, an outer saw blade and a drive mechanism, wherein the drive mechanism is further composed of a small output shaft, a large output shaft sleeved on the small output shaft, a first gearwheel, a second gearwheel and a power gear shaft, with said large output shaft being mounted in a box cover of the gearwheel box by means of a first and a second bearing, and said small output shaft being supported in an inner hole of said large output shaft and in a box body of the gearwheel box by means of a third bearing and a fourth bearing; said first gearwheel is sleeved loosely on said small output shaft by means of a fifth bearing, and fixed on said large output shaft; the second gearwheel is fixed on said small output shaft, and is arranged opposite to said first gearwheel; said power gear shaft extends into said machine head through a through-hole on the box body of the gearwheel box, with teeth on the power gear shaft engaging said first and second gearwheels respectively; and said inner and outer saw blades are fixed on said large and small output shafts respectively, wherein said small output shaft is designed with a first annular locking groove and a second annular locking groove located between said first gearwheel and second gearwheel, a first locking spring which presses against said fifth bearing being mounted in said first annular locking groove, and a second locking spring being mounted in said second annular locking groove, and at the same time a flexible piece which arches towards the side of said second locking spring is further sleeved on said small output shaft, one end of the flexible piece pressing against an end face of the second gearwheel and the other end pressing against said second locking spring.
In the above solution, an end face of said second gearwheel can have a recess thereon, with said flexible piece sitting in the recess, which serves to locate the flexible piece.
As a further improvement of the present utility model, said through-hole can be a stepped hole which narrows towards the side of said first and second gearwheels, a sixth bearing which supports said power gear shaft is located in a large hole of the stepped hole, and at the same time said power gear shaft has a step thereon which presses against an outer end face of said sixth bearing. In this way, the step on the stepped hole and the step on the power gear shaft can be used to effectively prevent the power gear shaft from moving towards the side of the first and second gearwheels, in order to ensure normal meshing between the gearwheels, reduced wear and smooth running.
In each of the above solutions, the following structure can be used as a fixing method between the inner saw blade and the large output shaft: a plurality of pin holes are distributed concentrically on an outer end face of said large output shaft, while the inner saw blade is provided thereon with through-holes corresponding to the plurality of pin holes, and pins are inserted into said pin holes after passing through the through-holes to achieve fixing of said inner saw blade to the large output shaft. This structure transmits the cutting force through three pin shafts, can ensure the coaxiality, perpendicularity and pulsation of the inner saw blade relative to the center of rotation, is convenient to manufacture and facilitates mass production. Of course, the following fixing method may also be employed: the outer end face of said large output shaft has a polygonal boss thereon, while said inner saw blade is provided thereon with a mounting hole which fits the boss closely, and said boss is inserted tightly into said mounting hole to achieve fixing of said inner saw blade to the large output shaft. This solution enables strict control of the concentricity, axial positioning and perpendicularity of the inner saw blade relative to the large output shaft, with the result that the inner saw blade cuts smoothly and the transmitted torque is large, and it also facilitates mass production.
By the same reasoning, the following structure can be used as a fixing method between the outer saw blade and the small output shaft: an outer end section of said small output shaft is produced with an integral platform for said outer saw blade to bear against, a plurality of pin holes being distributed concentrically on the platform, while the outer saw blade is provided thereon with through-holes corresponding to the plurality of pin holes, and pins after passing through the through-holes are inserted into the corresponding pin holes to achieve fixing of said outer saw blade to the small output shaft. Employing an integrally produced platform to replace the original inner pressure plate not only makes assembly convenient, but also reduces error, and thus the mounting position of the outer saw blade can be further ensured; moreover, such a solution in which the cutting force is transmitted through three pin shafts can likewise ensure the coaxiality, perpendicularity and pulsation of the outer saw blade relative to the center of rotation, and facilitates mass production. Of course, another structure may also be used as a fixing method between the outer saw blade and the small output shaft: an end section of said small output shaft is produced with an integral platform for said outer saw blade to bear against, with the platform having a polygonal boss thereon, the height of the boss being less than the thickness of the outer saw blade, and a screw hole being axially provided in the boss; a mounting hole matching the boss is provided on said outer saw blade, said outer saw blade is fitted over said boss by means of the mounting hole, a pressure plate is held against the outer side of said outer saw blade, and a screw is thread-connected in said screw hole after passing through said pressure plate to achieve fixing of said outer saw blade to the small output shaft. This solution can ensure that the outer saw blade is pressed tightly onto the boss and fastened to the small output shaft to form a single unit, such that minimum runout of the outer saw blade is maintained during rotation, with the result that the outer saw blade cuts smoothly and the transmitted torque is large, and it also facilitates mass production.
In the above solution, as a further improvement, said first bearing and third bearing are located in the same sectional plane, this cross-section being perpendicular to said small output shaft; such a solution helps to improve rigidity of support.
Compared to existing technology, the fact that two annular locking grooves and two locking springs are added in the present utility model means that the pressing of the first locking spring against the end surface of the fifth bearing can be utilized to prevent outward protrusion of the small output shaft, while retraction of the small output shaft can be prevented with the aid of the second locking spring; at the same time, the added flexible piece can not only absorb the cumulative tolerance arising in the manufacture of various components such as the gearwheel box, ensuring coincidence of the axial positions of the large and small output shafts after installation, but can also cause the small output shaft to have a tendency towards outward protrusion at all times, such that the small output shaft is preloaded in the axial direction, ensuring that the inner saw blade has a limited amount of space for sliding movement left and right; as a result, it can be ensured that there is an appropriate gap between the two saw blades at all times, such that the cutting operation may proceed smoothly and reliably.